The present invention relates to a pre-charging circuit for a plurality of sections of a DC voltage network, wherein said sections can be connected together and separated from each other individually or in groups via a respective switch element.
The present invention further relates to a DC voltage network,                wherein the DC voltage network has a plurality of sections,        wherein the DC voltage network has a switch element for each of the sections, via which the respective section can be connected to and separated from the other sections,        wherein the DC voltage network has such a pre-charging circuit.        
DC voltage networks are used in many cases for energy distribution within closed systems (for example within manufacturing installations). Energy distribution via DC voltage has a number of advantages over energy distribution via AC voltage. The exchange of energy between individual sections of the network is simpler, for example. In particular, reciprocal coordination of frequency and phase position of the individual sections is not required.
Such a DC voltage network usually consists of a plurality of sections, which can be separated from each other and connected together by a switch element in each case. Said sections can have the widest variety of energy sources (for example a photovoltaic installation) or energy stores (for example batteries) and the widest variety of consumer units. Also present in many cases is a connection via a voltage converter to a three-phase voltage network which feeds the DC voltage network. The connection to the three-phase voltage network can also be considered as a section within the meaning of the present invention.
When the DC voltage network is shut down or separated from the three-phase network, or when various sections of the DC voltage network are separated from each other, the situation can arise that the individual sections have differing voltages. In such instances, the sections must not be simply connected together since this would at least briefly result in extremely high equalizing currents.
In order to keep the equalizing currents low or even prevent these completely if possible, the sections can have capacitive energy stores which are pre-charged before the connection of a respective section to the other sections. The voltage of the respective section is thereby adapted so closely to the voltage of the other sections that the connection of the respective section to the other sections then results in only a low equalizing current.
In the prior art, pre-charging circuits are used to pre-charge the capacitive energy stores. For the purpose of pre-charging the capacitive energy store, a respective pre-charging circuit is customarily connected in parallel with the switch element for the respective section. The pre-charging circuit usually consists of a series circuit of an electronic or electromechanical switch and a resistor.
This solution according to the prior art has various disadvantages. Firstly, a dedicated pre-charging circuit is required for each section. Furthermore, electrical losses occur in the resistor when pre-charging. Furthermore, the capacity of the resistor must be adapted to the section of the DC voltage network to be charged in each case, both in relation to the maximum charging current and in relation to the power loss occurring in the resistor.
A further solution according to the prior art proposes the pre-charging of a section by means of a voltage source, for example an AC/DC converter or a DC/DC converter. In this case, the electrical losses can be reduced. However, a controllable converter is still required for each section. The converter must be fed from that section which is intended to deliver the required energy. This means that the configuration must be defined specifically for each DC voltage network. The capacity of the converter must be adjusted to the requirements of the section that is to be pre-charged, and to those of the section which feeds the section that is to be pre-charged.
The object of the present invention is to provide possibilities by means of which the pre-charging of the sections can be realized in a simple, efficient and economical manner.